Package-on-package (PoP) structures may include at least two device packages, with a top package 140 stacked above a bottom package 130. Each package may include one or more dies electrically coupled to a substrate. As shown in FIG. 1A, a bottom package 130 includes a first substrate 101 and a first die 110. As shown, the first die 110 may be a flip chip and may be bonded to the first substrate with an array of solder bumps 105. The top package 140 may include one or more dies, such as second and third dies 112, 114 that are electrically coupled to the second substrate 102. As shown, wires 143 may provide electrical connections from the dies 112, 114 to pads 113 on the second substrate 102. The second substrate 102 is electrically coupled to the first substrate 101 by interconnects. As shown in FIG. 1A, the interconnects are solder bumps 144. In addition to electrically coupling the second substrate 102 to the first substrate 101, the interconnects also provide the stand-off height HS that provides clearance to bond the second substrate 102 above the first die 110.
Prior art solutions for providing the desired stand-off height HS have used solder bumps 144 and through mold via drilling, as shown FIG. 1A. In package 190, solder bumps 144 are disposed over contact pads 118 on the first substrate 101. Prior to reflowing, a mold layer 165 may be formed around the solder bumps 144 to prevent the solder bumps 144 from slumping outwards and causing electrical short circuits between neighboring interconnects. Through vias 122 may then be drilled through the mold layer 165 to provide access to the solder bumps 144. However, to provide adequate stand-off heights HS, the diameters of the solder bumps 144 are substantially equal to the desired height HS. Accordingly, the widths of the solder bumps 144 limit the amount that the pitch PI can be reduced.
In order to reduce the pitch PI, prior art PoP structures have used discrete interposes 124, such as those shown in package 191 illustrated in FIG. 1B. Discrete interposers 124 may be organic or ceramic materials, such as silicon or glass. Through vias may be formed through the interposers and metal may be disposed therein. The metal may be a copper that is deposited with an electroless plating process. The discrete interposer may then be electrically coupled and bonded to the first and second substrates 101, 102 with solder bumps 107. While the pitch PI obtainable using discrete interposers 124 is smaller than the pitch PI obtainable with solder bumps 144, the cost to produce the discrete interposers is high.